首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1473473篇
  免费   119217篇
  国内免费   8170篇
耳鼻咽喉   18972篇
儿科学   47229篇
妇产科学   41635篇
基础医学   208018篇
口腔科学   38757篇
临床医学   134343篇
内科学   293587篇
皮肤病学   33911篇
神经病学   120282篇
特种医学   56259篇
外国民族医学   498篇
外科学   217077篇
综合类   43767篇
现状与发展   17篇
一般理论   488篇
预防医学   114319篇
眼科学   33310篇
药学   105083篇
  55篇
中国医学   6669篇
肿瘤学   86584篇
  2021年   14227篇
  2019年   13810篇
  2018年   18809篇
  2017年   14642篇
  2016年   16136篇
  2015年   19006篇
  2014年   26186篇
  2013年   36441篇
  2012年   50156篇
  2011年   53209篇
  2010年   31562篇
  2009年   29545篇
  2008年   47459篇
  2007年   50117篇
  2006年   50599篇
  2005年   49194篇
  2004年   45854篇
  2003年   43723篇
  2002年   41866篇
  2001年   74261篇
  2000年   75945篇
  1999年   63058篇
  1998年   18028篇
  1997年   16398篇
  1996年   16316篇
  1995年   15480篇
  1994年   14052篇
  1993年   12955篇
  1992年   46248篇
  1991年   43845篇
  1990年   41811篇
  1989年   39829篇
  1988年   36380篇
  1987年   35555篇
  1986年   33003篇
  1985年   31372篇
  1984年   23875篇
  1983年   20068篇
  1982年   12235篇
  1981年   10807篇
  1979年   20720篇
  1978年   14577篇
  1977年   12084篇
  1976年   11366篇
  1975年   11622篇
  1974年   13988篇
  1973年   13539篇
  1972年   12633篇
  1971年   11469篇
  1970年   10910篇
排序方式: 共有10000条查询结果,搜索用时 20 毫秒
991.
Multiphase radon generation and transport in porous materials   总被引:5,自引:0,他引:5  
Radon generation and transport in porous materials involve solid, liquid, and gas phases in the processes of emanation, diffusion, advection, absorption, and adsorption. Oversimplifications, such as representing moist soil systems by air-phase emanation and transport models, cause theoretical inconsistencies and biases in resulting calculations. Detailed Rn rate balance equations for solid, liquid, and gas phases were analyzed and combined using phase equilibrium constants to derive a single diffusive-advective rate balance equation in the traditional form. The emanation, diffusion, and permeability coefficients in the new equation have expanded definitions and interpretations to include Rn phase transfer. Radon adsorption was characterized by an exponential moisture dependence, and diffusion and permeability constants utilized previous moisture relationships. Correct boundary and interface conditions were defined, and the unified theoretical approach was applied to field data from a diffusion-dominated system and to laboratory data from an advection-dominated system. Measured 222Rn fluxes and concentrations validated the modeled values within the measurement variability in both applications.  相似文献   
992.
Thirteen patients with a malignant germ cell tumor of the ovary have been treated with a combination of vinblastine, bleomycin, and cisplatin (VBP). In 12 patients a complete remission was reached, which was maintained in 10 of these patients. One patient with large tumor residues and a partial remission became CR after surgery. The tumor recurred in 2 patients after 6 and 27 months. Overall, 11 of these patients are in long-term remission, from 14 to 84 months after the start of treatment. VBP is an effective treatment for malignant germ cell tumors of the ovary, even in patients with large tumor residuals.  相似文献   
993.
A patient with skeletal Class III malocclusion was treated in 2 phases during the early permanent dentition. In phase 1, maxillary protraction was combined with rapid palatal expansion; in phase 2, fixed appliances were placed. The results were good posttreatment, and, 1 year later, a favorable growth tendency could be observed. This report shows that treatment for a patient with skeletal Class III malocclusion can be started in the early permanent dentition, with very good final results.  相似文献   
994.
995.
There is limited information regarding oral health status and other predictors of oral health‐related quality of life. An association between oral health status and perceived oral health‐related quality of life (OHQOL) might help clinicians motivate patients to prevent oral diseases and improve the outcome of some dental public health programs. This study evaluated the relationship between older persons' OHQOL and their functional dentition, caries, periodontal status, chronic diseases, and some demographic characteristics. A group of 733 low‐income elders (mean age 72.7 ISD=4.71, 55.6% women, 55.1% members of ethnic minority groups in the U.S. and Canada) enrolled in the TEETH clinical trial were interviewed and examined as part of their fifth annual visit for the trial. OHQOL was measured by the Geriatric Oral Health Assessment Index (GOHAI); oral health and occlusal status by clinical exams and the Eichner Index; and demographics via interviews. Elders who completed the four‐year assessment had an average of 21.5 teeth (SD=6.9). with 8.5 occluding pairs (SD=4.6), and 32% with occlusal contacts in all four occluding zones. Stepwise multiple regressions were conducted to predict total GOHAI and its subscores (Physical, Social, and Worry). Functional dentition was a less significant predictor than ethnicity and being foreign‐bom. These variables, together with gender, years since immigrating, number of carious roots, and periodontal status, could predict 32% of the variance in total GOHAI, 24% in Physical, 27% in Social, and 21 % in the Worry subscales. These findings suggest that functional dentition and caries influence older adults' OHQOL, but that ethnicity and immigrant status play a larger role.  相似文献   
996.
BACKGROUND: Adjustable gastric banding is a popular bariatric operation in Europe. About 1500 patients per year undergo a such procedures in Germany. Clinical data on the rate of long-term complications such as pouch dilatation, slippage, and band migration are available in only a few long-term studies with small numbers of patients. Meta-analyses report on comordities and reduction in weight. The rate and management of long-term complications were examined at this inquiry. METHODS: Ninety hospitals were asked about rates of band implantation, follow-up, and complications. Thirty-eight hospitals (42.2%) participated in the study. The management of complications including slippage, pouch dilatation, and band migration was analyzed. RESULTS: At 35 hospitals, 4138 patients underwent gastric banding procedures in 25 hospitals over more than 5 years. The mean follow-up rate is presently 85.3%. Long-term complications were described in 8.6% of the patients. Pouch dilatation occurred in 5.0%, slippage in 2.6%, and band migration in 1.0%. CONCLUSIONS: Laparoscopic adjustable gastric banding can effectively achieve weight loss. However, band-related and functional complications influence late outcome. The rate of long-term complications was equivalent to that already in the literature.  相似文献   
997.
OBJECTIVE: To estimate the gestational age ranges that result in optimal birth outcomes for each of four risk-defined groups. STUDY DESIGN: Retrospective cohort study of singleton late third-trimester deliveries at a large urban teaching hospital between July 1995 and September 2003. Low-risk, advanced maternal age, hypertensive and diabetic patients were identified and grouped. Rates, by day of gestation at delivery, of cesarean delivery, major maternal perineal trauma, low 5-min APGAR score and NICU admission were determined for each study group. RESULTS: Each study group had meaningful changes in rates of obstetric outcomes as a function of gestational age at delivery and these patterns differed from group to group. A unique optimal time of delivery (OTD) was estimated for each group. The low-risk group OTD was calculated to be 37 weeks 1 day to 41 weeks 0 day; the advanced maternal age group OTD was 38 weeks 5 days to 39 weeks 6 days; the hypertension group OTD was 39 weeks 2 days to 40 weeks 1 day; and the diabetes mellitus group OTD was 40 weeks 3 days to 41 weeks 1 day. CONCLUSIONS: The OTD varied based on obstetrical risk. Strategies to increase the proportion of deliveries that occur within the OTD for specific risk-defined groups could theoretically improve birth outcomes.  相似文献   
998.
PURPOSE: Perineural invasion is a frequent occurrence in salivary adenoid cystic carcinoma (ACC) and may prevent complete surgical resection. Studies have indicated that nerve growth factor (NGF) and its high-affinity receptor tyrosine kinase A (TrkA) may play a role in perineural invasion in several malignancies in which perineural invasion is observed. The present study was conducted to investigate the expression of NGF and TrkA in salivary ACC and to examine the effects of NGF on adhesion, migration and invasion capacities of a salivary ACC cell line (SACC-83) in vitro. PATIENTS AND METHODS: Expression of NGF and TrkA was explored using immunohistochemistry in paraffin-embedded tissues of 32 cases of salivary ACC. The effects of NGF on in vitro adhesion, migration, and invasion capacities of the SACC-83 cell line were examined using an MTT assay and a modified Boyden chamber assay respectively. RESULTS: In ACC specimens, 31 (96.9%) and 32 (100%) tumors showed immunoreactivity for NGF and TrkA respectively. Significant correlations were found between NGF/TrkA expression levels and perineural invasion (P < .05). In cell adhesion assay, the percent adherences of SACC-83 cells co-cultured with 25 ng/ml NGF at 1.5 hours and 5, 25 ng/ml NGF at 6 hours were significantly higher than that co-cultured with 0 ng/ml NGF (P < .05). However, high concentration of NGF (500 ng/ml) resulted in a significant inhibition of invasion (P < .05). CONCLUSION: Overexpression of NGF and TrkA in human salivary ACC tissues may constitute a reason for perineural invasion in salivary ACC.  相似文献   
999.
Introduction     
Raymond C. Read 《Hernia》2006,10(6):454-455
  相似文献   
1000.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号